Keeping 20 around is a little excessive but it gives 390700800 possible wallets. So security can be trivially parameterized based on how secure you want your wallet to be if someone finds your stash.
Mid-level hardware can check 50k addresses per second, which means it would only take around 2 hours to check all possibilities. So please don't think this presents any kind of challenge to someone who finds your 20 pieces of paper and assumes you would only keep them if they are hiding your wallet ;)
Entropy-wise, simply using a strong RNG would provide a better result than relying on the printing company. Maybe they only print 35 different combinations and assume people don't eat Chinese food enough to notice?
If it's poor entropy and doesn't really provide any protection against being brute forced if found, I'm not sure why you would want to go this route :)
James